The best way around it is to use rescue.iso instead. Since rescue.iso
has stage2 on it, you can point it at any repo to do the install, like
your original F8 repo.

Sounds good. I can't find a rescue.iso under development at the
moment, though, so I'm going with (in order) trying to use rawhide
vmlinuz + initrd.img (replacing .buildstamp with the one from F8); and
if that doesn't work, actually replacing the F8 install kernel with
the rawhide installer kernel and ditto the modules in the initrd ...